Liquid compositions containing agents for chemical bleaching and disinfection are widely used for household or industrial cleaning, for personal cleansing products and in the pharmaceutical industry.
These compositions can contain, as active agents, hypochlorous acid salts, or hydrogen peroxide or peroxide precursors thereof.
Hypochlorite-based compositions have been the most used insofar due to their efficacy and low cost. Nevertheless, peroxides-based compositions are less aggressive and do not develop the unpleasant smell of chlorine or chloramines, therefore they are preferred for household use and personal hygiene.
The activity of hypochlorites- and peroxides-based compositions, i.e. their content of active chlorine or active oxygen, tends to decrease in time, which affects, as a consequence, other characteristics, such as colour and cleaning power. Modifications of the rheologic behaviour can also be observed if, as in most cases, rheologic modificators are contained for regulating the viscosity of the compositions.
The above drawbacks, which have prevented a wider diffusion on the market, occur mainly in hydrogen peroxide- or peroxides-based compositions, in particular at alkaline pH, where they show the most favourable detergent properties.
The cause of this instability is due to Fe+++, Cu++ and other heavy metal cations, which catalyse peroxide decompositions; since these cations are active even at p.p.m. concentration, it is difficult to keep them under control.
Several patents disclose stabilised compositions characterised in that the pH is carefully maintained under 7, in order to prevent instability.
In this respect, U.S. Pat. Nos. 4,839,156; 4,788,052; 4,839,157; 4,696,757; 4,238,192; 5,419,847 can be considered.
The use of more or less effective stabilising systems for obtaining compositions that are stable at alkaline pH is disclosed in other patents, such as U.S. Pat. No. 5,264,143, which discloses the use of phosphonate chelating agents; U.S. Pat. No. 4,900,468, which discloses the use of chelating agents in combination with substituted hydroxy benzenes as free radicals inhibitors; U.S. Pat. No. 6,083,422, which claims the use of rheologic stabilisers consisting of a series of variously substituted benzenes.